The present invention relates a dry chemical-mechanical polishing method for polishing and planarizing surface pattern on a product such as semiconductor wafer.
As one of the processes to manufacture semiconductor integrated circuit, there is a process for planarizing fine surface irregularities (convex and concave portions) on the surface of a semiconductor wafer prior to interconnection process. In this process, a chemical-mechanical polishing (CMP) system is used. This chemical-mechanical polishing system is the same as a general type mechanical polishing system as commonly used except that a solution containing components exerting chemical action to semiconductor wafer is used as a polishing solution. FIG. 4 is a cross-sectional view showing general features of a conventional type chemical-mechanical polishing system. On an output shaft 402 of a motor 401, a rotary tool 403 is mounted. On the surface of the rotary tool, a polishing pad 404 made of a material suitable for polishing is attached. A semiconductor wafer 407 is mounted on a rotary holder 406, which is attached on a rotation shaft 405, and a supply nozzle 409 for supplying a polishing solution 408 is provided above the polishing pad.
In this polishing system, the rotary tool and the semiconductor wafer are rotated and are pressed against the polishing pad, and suspended polishing solution is supplied onto the polishing material via the supply nozzle. As a result, the surface of the semiconductor wafer can be polished.
JP-A-9-232257 discloses a method, which also uses a polishing solution. In this method, however, instead of abrasive grains or powder, a grinding stone comprising abrasive grains buried in a polishing material on the surface of the rotary tool is used. For example, in case an oxide film is polished, a grinding stone is used, which comprises a phenol resin with silicon disulfide, cerium oxide, alumina, etc. of about 0.01 to 1 xcexcm in grain size buried in it. By this method, the amount of abrasive grains can be reduced.
Further, U.S. Pat. No. 6,057,245 describes a planarizing technique in vapor phase. This method uses plasma, and a polishing pad is at a position opposite to the plasma. Also, abrasive grains are supplied in vapor phase.
All of the conventional wet type polishing method have the following drawbacks. First, running cost required for polishing is high. Large quantity of expensive polishing solution (abrasives and solvent) is used. Moreover, the polishing pad is very susceptible to clogging because of solid slurry. It is necessary to frequently perform conditioning of polishing surface and component replacement, and higher cost is required.
In terms of uniform planarizing from macro viewpoint, the speed on wafer edge is not uniform. Edge exclusion is between 3 mm and 5 mm and is not sufficient for uniform planaring. In terms of uniform planarizing seen from micro viewpoint, polishing selectivity of convex portions on the surface is not strict. As a result, concave portions on the surface are also scraped off. Further, difference between iso-pattern and densi-pattern is found in a range which is not negligible. Further, the interconnect metal may be corroded due to residual chemical substances such as acidic solvent or alkaline solvent during polishing operation because chemical action of the polishing solution is utilized for polishing. When metal component is present on the polished surface, electrochemical corrosion (electrolytic corrosion) may be induced. In such case, abnormal polishing of metal portion may occur. Detailed description will be given now on the electrolytic corrosion. As described in JP-A-2000-40679, when light enters pn junction provided on a silicon substrate, due to photovoltaic effect of silicon, short-circuit current flows through a closed circuit, which is formed by a polishing slurry attached between pn junction terminal formed in a wafer and wherein pn junction terminal is comprised of Cu connected to n-side (xe2x88x92side) of pn junction xe2x88x92pn junction xe2x88x92Cu connected to p side (+side) of the pn junction. From the surface of Cu interconnect connected to p side (+side) of the pn junction, Cu2+ ions are dissociated, and this causes electrolytic corrosion. As a result, abnormal polishing occurs on Cu surface.
Because of the structure of the system and the condition of polishing, it is very difficult to detect an end point where removal of the polishing layer is completed, and this leads to difficulty of in-line monitoring. Further, polishing solution and the polishing pad are optimized to a certain type of film material, and it is difficult to continuously polish a wide variety of film types. Further, the conventional polishing methods are generally based on wet process. Even when etching or CVD is performed under vacuum condition, a series of steps are required to take out the product to the atmospheric air and then to return it to the vacuum system. This often leads to the decrease of the throughput. These problems must be overcome, and it is also necessary to prevent damages such as scratches, and to maintain basic polishing performance to produce a flattened surface from the surface with pattern of larger dimension and with pattern of fine dimension.
Further, according to the dry polishing method as described in the above U.S. Pat. No. 6,057,245, the polishing pad is positioned opposite to the plasma, and no special care has been taken on the execution of the etching with high efficiency.
It is an object of the present invention to provide a dry chemical-mechanical polishing method, by which the etching can be performed with high efficiency.
To attain the above object, the dry chemical-mechanical polishing method according to the present invention comprises the steps of bringing surface of a polishing specimen retained on a specimen stand into contact with a polishing tool while supplying plasma from a plasma source, moving the relative positions of the polishing specimen and the polishing tool and then polishing, and planarizing the surface of the polishing specimen, whereby at least a part of the surface of the polishing specimen is exposed to an atmosphere of plasma during said polishing operation.
In order to lead to such condition that at least a part of the surface of the polishing specimen is exposed to an atmosphere of plasma during polishing operation, size of the surface of the polishing specimen should be made larger than that of the polishing tool. If these two are both designed in circular shape, diameter of the polishing specimen should be made larger than diameter of the polishing tool. In case these two have the same size or when the polishing tool is larger, it should be designed that the polishing tool is protruded from the polishing specimen. In this case, the polishing tool may not be necessarily protruded from the polishing specimen during the polishing operation, but it is preferable that it is always protruded. Also, if it is designed in such manner that holes are provided on the polishing tool and plasma is injected from inside the polishing tool, at least a part of the surface of the polishing specimen is exposed to the atmosphere of the plasma regardless of the size of the polishing specimen or the polishing tool.
To attain the above object, the dry chemical-mechanical polishing method according to the present invention comprises the steps of exposing at least a part of surface of a polishing specimen retained on a specimen stand and adsorbing radicals on the surface of the polishing specimen, bringing polishing means into contact with the surface of the polishing specimen, moving relative position of the polishing specimen and the polishing means, heating convex portions of the surface of the polishing specimen by friction, and polishing said convex portions, and planarizing the surface of the polishing specimen.
In all of the above methods, the polishing atmosphere may be under reduced pressure or below atmospheric pressure, or under pressure higher than the atmospheric pressure. More preferably, the pressure of the polishing atmosphere should be in the range from 1 Pa to approx. 100,000 Pa.